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has a strongly curved beak, tiny teeth at the umbo, and is a soHd rosy-brown on the inside. Mytilus plicatuhis Lamarck is this species. The subspecies deriiissus granosissiimis Sowerby (both sides of Florida to Texas and Yucatan) is very similar but with almost twice as many ribs which are finely and neatly beaded. Common. Modiolus forjjicatus Carpenter California Horse Mussel Plate 29-0 Monterey to San Pedro, California. About I inch in length, smoothish, inflated, light-brown periostracum which wears white at the beak end. Beaks curved strongly forward. Inte- rior dull white. Found in moderately deep water, and rarely cast ashore. Associated with Haliotis rufescens. /Modiolus capax Conrad Capax Horse Mussel Santa Cruz, California, to Peru. 2 to 6 inches in size. Periostracum thick, often with coarse hairs, chestnut-brown in color. Worn shell brick-red with bluish mottlings. In- terior half white, half (ventral) brownish purple. Resembles figure of Modiolus americanus (PI. 35I). Genus Brachidontes Swainson 1840 Subgenus Brachidontes s. str. Brachidontes citriniis Roding Yellow Mussel Plate 35! Southern Florida and West Indies. I /<i inches in length, elongate, with numerous wavy, fine axial ribs, col- ored a light brownish yellow outside, and inside mottled a metallic purplish and white. Anterior end has four very tiny white teeth. Bordering the liga- ment are about 30 very small, equal-sized teeth on the edge of the shell. Com- pare with B. exustus Linne which is wider. The genus is commonly mis- spelled Brachy domes. Subgenus Horinomya Morch 1853 Brachidontes exustus Linne Scorched Mussel Plate 35) North Carolina to the West Indies. % inch in length, rather elongate with numerous fine axial ribs; colored a yellowish brown to dark-brown outside, and inside mottled with a metallic